3.5.6. Findings Regarding Driving Forces

Herein, some of the many specific factors that affect scenarios of land-use
emissions have been discussed. From a correlation analysis that compared the
influence of changing population, economic activity, and technological change
on land-use emission scenarios, Alcamo and Swart (1998) concluded that population
was the most influential driving force. The reason is the relationship between
population and increasing food demand, which leads to more cows that produce
CH4 and more extensive fertilized croplands that release N2O. Although most
scenarios also assume that improvements in crop and animal productivity will
partly compensate for increasing food demand, some authors do not believe that
productivity increases can be sustained. For example, Kendall and Pimentel (1994)
show a decrease, rather than increase, in per capita grain production because
of less optimistic assumptions about the increase in crop productivity (0.7%
per year). Brown and Kane (1995) point out some developments that may slow down
productivity:

The backlog of unused agricultural technology (and hence the potential for
further agricultural productivity increases) is shrinking.

Demands for water are reducing the ability of the hydrologic cycle to supply
irrigation water.

In many countries, the use of additional fertilizer on current crop varieties
does not significantly increase their yields.

Industrial countries are losing fertile land to urbanization.

Brown and Kane (1995) argue that in recent years rice yields have either stabilized
or fallen in many key rice-producing countries, and suggest that dramatically
boosting rice yields above a level of 4 tons per hectare may require new technological
advances. If the skeptics are right, and the assumed productivity increases
of the "business-as-usual" scenarios are not realized, then a greater expanse
of cropland would be needed to satisfy the same agricultural demand. This expansion
would lead to still higher emissions of CH4 from rice fields and livestock,
and more rapid deforestation and earlier peaks in the emissions of CO2 . However,
the lower increase in productivity probably also implies lower fertilizer use
per hectare, which may lower emissions of N2O from fertilized soils.